Wheelchairs are a widespread and very successful assistive technology for people with disabilities, with evolved designs that enable activities of daily living and promote participation [1, 2]. “Ultralight” manual wheelchairs are a class of high-performance, rigid wheelchairs that typically weigh under 11 kg (25 lbs.) with wheels [3] and offer a rigid, responsive wheeling performance. Typical users of ultralight rigid wheelchairs are independent active members of the community, with disabilities such as paraplegia, low tetraplegia, spina bifida, lower limb amputation, and cerebral palsy. These people tend to use their wheelchairs for large parts of the day, relying on them for most of their personal mobility needs. Perhaps the biggest functional benefits afforded by ultralight wheelchairs are in “transfer” weight—chair weight without wheels. This is the mass that users must lift over their body as they place the wheelchair frame into their vehicle after a transfer. Transfers are one of the highest-scored essential mobility skills for daily life [4]. Propulsion also benefits from low chair weights, although one can argue that rigidity and centre of mass are as important to wheeling performance: e.g. sports wheelchairs often weigh over 18 kg (40 lbs.) [5].
While ultralight wheelchairs are optimized for wheeling, people typically spend only about 10% of their seated occupancy time in their wheelchair actually wheeling [6]. Ideally, a wheelchair would support optimized wheeling, and at the same time support other activities of daily living and better health. The Elevation™ wheelchair [7] helped introduce the concept of “dynamic wheeled mobility” to ultralight wheelchairs, offering previously unavailable “on the fly” seat height adjustment and backrest recline adjustments to the user such that various activities performed throughout the day can be matched by an appropriate seat position [8]. It is thought that use of dynamic seating may mitigate some of the health issues associated with chronic wheelchair use such as: pain and discomfort; pressure-induced tissue damage; joint immobility and contractures; spasticity; and musculoskeletal issues associated with arm propulsion [9-13]. Participation in the community may also be beneficially impacted by dynamic seating [12, 13]. A preliminary study about the use of the Elevation™ wheelchair showed that more frequent adjustments of the seat elevating feature were correlated positively with higher satisfaction with participation in the community and engagement in a wider variety of activities [14]. It is clear that changing one's position often is more beneficial than maintaining a fixed position. The tradeoff with this seat adjustability is added weight, although the Elevation™ wheelchair currently available on the market starts at a weight of only about 10 kg (22 lbs.) including wheels. Other manual wheelchairs with dynamic seating functions are not suitable for all-day use by active users (except in specialized situations), as these chairs (conventional tilt/recline, or standing wheelchairs) typically weigh in excess of 18 kg (40 lbs.).
In a paediatric use scenario, “on the fly” adjustments of front and rear seat height might be particularly advantageous. A child would derive significant benefit from raising their seat in order to be more functional and interactive with others. And lowering the seat, including the front of the seat, affords more function and interactive opportunities for a child.
The ability to stand up from a seated position is fundamental to numerous daily activities, however it can present challenges for many with people with mobility impairments. For wheelchair users, this task is complicated by footrests that must be cleared from the front of the wheelchair prior to standing. To do this independently, a user must lean forward towards the ground to swing the footrests away. This is physically challenging or impossible for many users, particularly for seniors with limited flexibility and compromised balance.
Accordingly, it is desirable to improve the sit to stand (STS) activity often performed by some wheelchair users who have residual standing (and perhaps ambulation) function. Prior to exiting or entering a manual wheelchair, a user typically has to lean down and either swing away the footrest hangers to the side, lift the footrests to the vertical retracted position, or often both. Either motion can be difficult for some manual wheelchair users, particularly those with limited upper extremity mobility and/or limited forward leaning flexibility. Consequently, these users will constantly require help from caregivers to retract the footrest before they get in and out of wheelchairs. Retracting the footrests is also an awkward task for caregivers, who will have to bend over or crouch to raise the footrests. Additionally, physical contact with the footrests can be undesirable due to accumulation of dirt and potentially infectious agents onto the footrests over time. Thus, it would be a beneficial method for improving STS in wheelchairs to not have to move the footrests during the STS activity.
It is also desirable sometimes to have a mechanism to fully stand while supported in the wheelchair. This style of wheelchair is usually called a standing wheelchair. In this situation, a user would not walk away from the wheelchair, rather they would raise the rear of the seat towards a near vertical position while standing firmly on the footplate. Straps at various locations, including the knees, would secure the person into the wheelchair. A stability mechanism is also used to prevent unsafe forward tilt of the wheelchair in the standing position.